In co-pending application Ser. No. 08/384,795 filed Feb. 6, 1995, now U.S. Pat. No. 5,529,190 (the disclosure of which is hereby incorporated by reference herein), a gas sparged hydrocyclone foam separation system is disclosed for use in a deinking process in the production of paper products from recycled paper. The hydrocyclone is used as a contactor rather than a deinker per se and is associated with a foam separation vessel. The present invention relates to further refinements of such a system which retains the major advantages of that system [e.g. allowing large volumes of air to be utilized without disruption of the system, for example air-to-stock ratios of between about 0.5 and 0.75:1, or even as high as about 1.5:1] while also providing a number of different modifications that facilitate commercialability of such a system and enhance its efficiency of operation, minimize floor space per unit deinking capability, and enhance ease of access and utilization.
In comparison testing of a system according to the present invention with respect to conventional froth flotation equipment, it has been found that operation of the system according to the invention is more effective. For example in tests where a single stage system according to the present invention is used before conventional froth flotation units, the system of the invention produced an average brightness gain of 3.1 ISO points at a mean solid reject rate of about 2.7%, with a total particle removal efficiency of 65% with a usable fiber reject rate of only about 0.73% of the solids fed to the stage. Reject consistency-to-feed consistency ratios typically range from 1:1 to 4:1 with a mean ratio typically being about 2:1. For example, for an average feed consistency of 1.3%, the average reject consistency is about 2.6%. When used after conventional froth flotation, a system according to the invention had an average ISO gain of about 1.7 points, with an additional 32% reduction in total particles with a solid reject rate average of about 1.7% and with a usable fiber loss average of about 0.34%. Data compiled from testing of systems according to the invention indicate that two stages of flotation utilizing the present invention will provide the equivalent performance of four conventional froth flotation cells on total particle reduction, and provide approximately 1 ISO point more brightness.
According to one aspect of the present invention a deinking system, for deinking a slurry (typically recycled paper pulp produced in a pulper such as a FIBERFLOW.RTM. Drum such as sold by Ahlstrom Kamyr of Glens Falls, N.Y., and by various subsequent treatments) is provided. The system according to the invention comprises the following components: A plurality of gas sparged hydrocyclones, each having first and second ends, a tangential slurry inlet adjacent the first end, and a slurry outlet adjacent the second end. A foam separation vessel having an outer periphery, a liquid level therein, a top, and a bottom. The plurality of gas-sparged hydrocyclones mounted around the outer periphery of the foam separation vessel. A slurry accepts outlet from adjacent the foam separation vessel bottom. A conduit connecting each of the slurry outlets of the hydrocyclones to the foam separation vessel and having a discharge opening passing through the outer periphery and below the liquid level in the foam separation vessel and above the accepts outlet of the foam separation vessel. And, means for removing foam at or above the liquid level, with ink particles and contaminants therein, from the foam separation vessel.
Each of the hydrocyclone discharge openings into the foam separation vessel outer periphery are preferably tagentially directed so as to create a bubble separation-facilitating internal rotation within the foam separation vessel. The means for removing the foam preferably comprises a rejects trough adjacent the top and outer periphery of the vessel, having a bottom that slopes to one or more drain outlets, and preferably also including a stationary or movable liquid spray head. The bottom of the rejects trough may also be helical in shape and spiral downward to a single rejects outlet. Typically, the foam separation vessel is substantially cylindrical with a substantially circular cross-section, and in that case the rejects trough is--whether outside or inside the outer periphery of the vessel--annular. The plurality of hydrocyclones are typically at least three hydrocyclones spaced substantially evenly around the foam separation vessel outer periphery. Also a substantially annular operating platform may surround the outer periphery of the vessel adjacent the top thereof, positioned to allow an operator ready access to the hydrocyclones and foam removing means. A substantially annular header surrounding the vessel outer periphery and connected to each of the hydrocyclone slurry inlets is preferably also provided. A slurry rotation breaking baffle assembly may be mounted at the slurry accepts outlet of the foam separation vessel.
Each of the hydrocyclones may be mounted at least in part by the vessel with the first end above the second end. The first end of each hydrocyclone typically includes a combination vent/foam rejects conduit, the foam rejects conduit having an outlet opening directed into the rejects trough of the vessel.
Each of the hydrocyclones may comprise an inner, gas-pervious cylinder surrounded by a solid wall cylinder defining an annular air jacket, and a single gas inlet being provided for supplying gas through the solid wall cylinder into the air jacket. The hydrocyclones are is preferably "pedestal-less", that is, it is preferred that the hydrocyclone outlet not contain a restriction such as an annular orifice The hydrocyclones also preferably include a deflector positioned in the sir jacket for causing a directed flow of gas from the single gas inlet to be dispersed in the air jacket and not directly impact the inner gas-pervious cylinder. If desired at least one conical substantially uniform back pressure generator (e.g. a pair of conical elements disposed in an hourglass-simulating relationship) may be disposed in each of the hydrocyclone slurry outlets.
The system may further comprise foam conveyance and breaking means associated with the drain outlet from the trough. Such means includes a downwardly extending outlet conduit, at least one liquid shower spray head below the trough bottom directed into the outlet conduit, and an upwardly extending vent conduit from the outlet conduit. A number of different configurations of this arrangement may be provided.
Also a foam and reject handling tank may be connected at a top portion thereof to the outlet conduit. Such a tank includes a substantially spiral downwardly extending feed ramp having an inner shoulder, an outlet from a bottom portion of the tank, and spray shower heads for spraying liquid into rejects on the ramp for breaking up foam bubbles.
According to another aspect of the present invention a deinking system is provided comprising the following components: At least one gas sparged hydrocyclone having first and second ends, a tangential slurry inlet adjacent the first end, a slurry outlet adjacent the second end, a gas-pervious inner cylinder between the first and second ends surrounded by a solid wail cylinder, defining an air jacket, and a single gas inlet for supplying gas through the solid wall cylinder into the air jacket. A foam separation vessel having a liquid level therein, a top and a bottom. A slurry accepts outlet from adjacent the foam separation vessel bottom. A conduit connecting the hydrocyclone slurry outlet to the foam separation vessel and having a discharge opening located within the outer periphery and below the liquid level in the foam separation vessel, and above the accepts outlet of the foam separation vessel. Means for removing foam at or above the liquid level, with ink particles and contaminants therein, from the foam separation vessel. And, a deflector positioned in the air jacket for causing a directed flow of gas through the single inlet to be dispersed in the air jacket and not directly impact the inner gas-pervious cylinder. It is preferred that the hydrocyclone is pedestal-less and further comprises a vent/foam rejects outlet from the first end.
The invention also relates to a gas sparged hydrocyclone comprising the following elements: A first end having a tangential slurry inlet adjacent thereto for introducing slurry with a swirling action. A second end having a slurry outlet adjacent thereto. A gas-pervious inner cylinder between the first and second ends surrounded by a solid wall cylinder, defining an air jacket. A single gas inlet for supplying gas through the solid wall cylinder into the air jacket. And, a deflector positioned in the air jacket for causing a directed flow of gas through the single inlet to be dispersed in the air jacket and not directly impact the inner air-pervious cylinder. The hydrocyclone is preferably pedestal-less, and it comprises a vent/foam rejects outlet from its first end.
The uniform back pressure generator, foam conveyance and breaking means, and foam and reject handling tank, as described above, are also novel.
It is the primary object of the present invention to provide for the effective deinking of slurry using a gas sparged hydrocyclone as a contactor, allowing highly efficient deinking compared to conventional froth flotation. This and other objects of the invention will be clear from the detailed description of the invention, and from the appended claims.